1. Technical Field
The invention relates to a device and a method for the noise-dependent adjustment of a desired acoustic signal radiated at a monitoring point.
2. Discussion
When music or speech is offered in a noise-filled environment via an electro-acoustic system, pleasurable hearing is generally muddied by the background noise. A noise-filled space in which music and speech are frequently heard is, for instance, the passenger compartment of a motor vehicle. The background noise can originate from the engine, the tires, the blower and other units in the motor vehicle and be a function of the speed, road conditions and the operating conditions in the motor vehicle. The occupant of the motor vehicle reacts to this time-varying backdrop by accordingly turning the volume control to adjust the desired signals offered in the form of music or speech.
For example, a method and a device for the dynamic optimization of sound are known from U.S. Pat. Nos. 5,434,922 and 5,615,270, both entitled xe2x80x9cMethod and Apparatus for Dynamic Sound Optimization.xe2x80x9d These patents disclose a method and device in which the volume of the desired signal is automatically adjusted as a function of the background noise. With it, the overall sound in the monitored space is evaluated in such a manner by means of a microphone so that the signal corresponding to the overall sound is fed to an extractor which extracts the noise-signal component from the overall sound. In a subsequent amplification-evaluation stage, this extracted noise-signal component is compared with the original signal from the sound source. The results of this comparison are then used for setting the volume of the desired acoustic signal.
What is problematic with this device and the method on which it is based, however, is that extracting of the noise-signal component does not entirely succeed, so that components of the desired signal are also contained in the extracted noise-signal component. Thus, the entire device is based on a noise level which is higher than the actual noise level. However, a higher volume is set which increases the volume. The effect of a higher volume set is that the desired-signal component remaining in the extracted noise-signal component also increases. This phenomenon, also described as xe2x80x9cgain chase,xe2x80x9d would thereby end in the maximum possible volume level, so that either the listener positioned in the motor vehicle must manually intervene in the event orxe2x80x94as in U.S. Pat. Nos. 5,434,922 and 5,615,270 implement a considerably more expensive system in order to suppress the xe2x80x9cgain chase.xe2x80x9d
Therefore, a principal object of the present invention is to provide a device and a method for the noise-dependent adjustment of a desired acoustic signal radiated at a monitoring point in which the gain-chase effect is reduced. In that way, an automatic increase in volume is reduced.
In is a further object of the present invention to provide such a method and device that improves over accuracy of prior art methods and devices and which is cost effective and efficient.
The foregoing objects of the present invention are achieved by a device having a signal source for the generation of a desired electrical signal as well as a signal-processing apparatus that are connected in series at the output end of the signal source and are adjusted by means of a control signal for the generation of a processed desired electrical signal. Furthermore, a sound-converting apparatus is connected in series at the output end of the signal-processing apparatus for the generation of the desired acoustic signal from the processed desired electrical signal, and a sound pickup for the generation of an electrical monitoring signal from the desired acoustic signal on which an acoustic noise signal is superimposed, are provided at the monitoring point.
Finally, an extractor is connected in series at the output end of the sound pickup for the purpose of extracting the noise-signal component contained in the monitoring signal. Connected in series at the output end of the extractor, in turn, is a controlling apparatus which receives the noise component of the monitoring signal and at least one additional signal derived from the monitoring signal, and which generates from both, the control signal for the signal-processing apparatus.
More particularly, at least one additional signal derived from the monitoring signal corresponds preferably to the sum of the desired-signal component and a spurious-signal component and/or the desired-signal component of the monitoring signal. Also, a signal derived from the monitoring signal can also be provided by the extractor.
Furthermore, a state signal can be applied to the controlling apparatus. With it, the volume and/or other variables of the desired signal can be influenced by additional information, e.g., not only from the volume setting (by means of the volume control, for instance) but also, in the case of installation in motor vehicles, from the vehicle speed and engine speed, for example.
The extractor preferentially has at least one adaptive filter. This can, for example, function according to the least mean square method.
For extracting the noise-signal component from the monitoring signal, the extractor can be connected to the signal source, from which it receives the desired signal, or be connected to the signal-processing apparatus, from which it receives the processed desired signal.
The method according to invention appropriately provides for the generation of a desired electrical signal, the processing of it as a function of a control signal, and the generation of the desired acoustic signal from the processed desired electrical signal. With that, an electrical monitoring signal, defined by the desired acoustic signal on which an acoustic noise signal is superimposed, is audited at the monitoring point; the noise-signal component contained in the monitoring signal is then extracted; and the noise-signal component contained in the monitoring signal is combined with a signal derived from the monitoring signal, producing the control signal.
Signals derived from the monitoring signal can, in turn, correspond to the sum of desired-signal component and spurious-signal component of the monitoring signal and/or to the derived from the monitoring signal, i.e., the desired-signal component.